Expression analysis suggests novel roles for members of the Pht1 family of phosphate transporters in Arabidopsis

The completion of the Arabidopsis thaliana genome has revealed that there are nine members of the Pht1 family of phosphate transporters in this species. As a step towards identifying the role of this gene family in phosphorus nutrition, we have isolated the promoter regions from each of these genes, and fused them to the reporter genes beta-glucuronidase and/or green fluorescent protein. These chimeric genes have been introduced into A. thaliana , and reporter gene expression has been assayed in plants grown in soil containing high and low concentrations of inorganic phosphate (Pi). Four of these promoters were found to direct reporter gene expression in the root epidermis, and were induced under conditions of phosphate deprivation in a manner similar to previously characterised Pht1 genes. Other members of this family, however, showed expression in a range of shoot tissues and in pollen grains, which was confirmed by RT-PCR. We also provide evidence that the root epidermally expressed genes are expressed most strongly in trichoblasts, the primary sites for uptake of Pi. These results suggest that this gene family plays a wider role in phosphate uptake and remobilisation throughout the plant than was previously believed.